New Delhi, Sep 5 (IANS): Prime Minister Narendra Modi on Thursday expressed grief over the loss of lives in an explosion at a firecracker factory in Punjab's Gurdaspur district on Wednesday.

"The tragedy at a firecracker factory in Punjab is heart-wrenching. Deeply anguished due to it. My condolences to the families of those who lost their lives. I hope the injured recover at the earliest. Agencies are working on rescue operations at the site of the tragedy," the Prime Minister's Office tweeted.

At least 21 people were killed and 26 injured in an explosion following a blaze at an unauthorised firecracker manufacturing unit in a densely-populated residential area in Batala town of Gurdaspur. The dead included the firecracker manufacturing unit's owner and six of his family members.

Seven grievously injured were referred to the Guru Nanak Hospital in Amritsar.

A number of nearby buildings, including a car workshop, were badly damaged in the explosion. An elderly woman and her grandchild, who were passing close to the disaster spot, were among the dead.